1. Field of the Invention
The present invention relates generally to an alternate source of energy. More particularly the present invention relates to a modification to a Savonius wind turbine rotor for converting kinetic energy in the wind to shaft power.
2. Background Art
Shaft power has been derived from the wind for centuries. Dutch windmills were first used for grist, and later converted to raising water to sea level for land reclamation. Wind power was commonly harnessed across the prairie and plains states in the U.S. for pumping water from wells. In the early part of the 20th century, wind was utilized for converting kinetic energy to electrical energy.
The last quarter of the 20th century saw a marked increase in interest in converting wind energy to shaft power. Many units from that era were horizontal shaft wind turbines using airfoils of various types. Drawbacks of such an arrangement are the need to have the power unit (generator, air compressor, etc.) on top of the tower with the airfoils, or the need for gearing to transfer the power toward the ground.
Efforts have been made toward improving vertical-shaft wind turbines as well. The Darius rotor utilizes airfoils in a fashion quite different than the horizontal shaft units. However, the Darius rotor is not self-starting, so a starting scheme is required.
The Savonius rotor is a self-starting, low-speed, vertical axis wind turbine (the axis need not be vertical, however, that is the usual configuration). However, in its traditional form (see FIG. 1), the Savonius rotor is known to exhibit low efficiencies. It is known as a drag-type wind turbine, as opposed to the lift-type wind turbines having horizontal axes and the Darius rotor. Rotation of the Savonius rotor is effected through momentum transfer from the air. The momentum of the air changes as its path is curved by the vanes of the Savonius rotor. Momentum exchange occurs on entrance to the vanes and on exit from the vanes. The change in momentum with time results in forces that tend to turn the Savonius rotor on its axis of rotation.
A modification to the Savonius rotor of FIG. 1 was disclosed in U.S. Pat. No. 5,494,407. The blades of this invention have been altered from half-circles in cross-section as seen in FIG. 1 to the shape shown in FIG. 2, having a linear portion nearer the axis of rotation and a curved portion, which is substantially an arc of a circle tangent to the linear portion and tangent to the circle defining the rotor diameter.
Another modification to the Savonius rotor of FIG. 1 is revealed in U.S. Pat. No. 6,283,711 wherein an additional, outer vane that is pivotally attached to the original, semicylindrical blade at the latter's leading edge.
A novel modification to the traditional Savonius rotor is shown in FIG. 3 wherein the vanes are reduced in size away from a vertical center such that they reach apexes at the top and bottom of the unit. Such a wind turbine can be made of light fabric material.
In all the prior art, the air flows into the cavity created by a vane, then is directed along a path that is substantially parallel to the vane until it exits the first vane and enters the second vane. The streamlines are, again, substantially parallel to this second vane. The air is finally exhausted downstream of the wind turbine to the freestream. None of the prior art discloses an exhaust port to permit air to exit the first vane without traveling through the second vane.
In addition, the known prior art does not reveal the use of Savonius rotor vanes as a surface on which to apply a solar panel.
There is, therefore, a need for an improved exit path for air to exhaust from a vane in a Savonius rotor. There is an additional need for the use of Savonius rotor vanes as a surface on which to apply solar panels.